SetDefault sets the default mux on the package for use in parsing params
we could instead decorate each request with a reference to the Route
but this means extra allocations for each request,
when almost all apps require only one mux.

type Mux struct {
// See httptrace for best way to instrumentErrorHandlerErrorHandlerFuncFileHandlerHandlerFuncRedirectWWWbool// contains filtered or unexported fields
}

Mux handles http requests by selecting a handler
and passing the request to it.
Routes are evaluated in the order they were added.
Before the request reaches the handler
it is passed through the middleware chain.

GetInt returns the first value associated with the given key as an integer.
If there is no value or a parse error, it returns 0
If the string contains non-numeric characters, it is truncated from
the first non-numeric character.